[Effects of Straw Returning on Soil Ammonia Volatilization Under Different Production Conditions Based on Meta-analysis].

In order to explore the response of Chinese farmland soil ammonia volatilization to straw returning to the field under different production conditions, this study used no straw returning as a control. Through the collection of published literature test data, the Meta-analysis method was used to quantitatively study the effects of different natural factors and, under the conditions of farmland management measures, the effect of returning straw to the field on the emission reduction of soil ammonia volatilization. At the same time, through partial correlation analysis, the main influencing factors of ammonia volatilization under the condition of returning straw to the field were found, and the ammonia volatilization was quantified. The results showed that the effect of straw returning on soil ammonia volatilization decreased with the increase in accumulated rainfall during the growth period and increased with the increase in average temperature during the growth period. When the soil pH was less than 6, straw returning to the field significantly promoted soil ammonia volatilization, and when the pH was ≥ 6, returning straw to the field significantly inhibited ammonia volatilization in the soil. The reduction effect of returning straw to the field on soil ammonia volatilization increased with the increase in soil clay content. When the total soil nitrogen content was <0.1% and >0.2%, returning the straw to the field significantly inhibited the volatilization of soil ammonia, and when the total soil nitrogen content was between 0.1% and 0.2%, returning the straw to the field significantly promoted the volatilization of ammonia from the soil. When the nitrogen application rate was 60-180 kg·hm-2 and the nitrogen application rate was >240 kg·hm-2, returning straw to the field significantly reduced soil ammonia volatilization (P<0.05), and when nitrogen application rate was 180-240 kg·hm-2, returning straw to the field significantly promoted ammonia volatilization in the soil. Returning straw to the field by plowing or rotary tillage significantly inhibited ammonia volatilization in the soil, whereas returning straw to the field in a mulching mode had no significant effect on ammonia volatilization. When the straw C/N>45, it significantly inhibited ammonia volatilization from the soil, and when the straw C/N ≤ 45, the straw returning to the field significantly promoted the ammonia volatilization of the soil. The reduction effect of straw returning on ammonia volatilization increased with the increase in straw-returning amount. In non-paddy fields, returning straw to the field had a significant inhibitory effect on soil ammonia volatilization, and in paddy fields, returning straw to the field had a significant effect on soil ammonia volatilization. The results of partial correlation analysis showed that in paddy fields, the average growth period and soil pH were the main factors affecting soil ammonia volatilization under the condition of returning straw to the field, and in non-paddy fields, nitrogen application rate and straw C/N were the main factors affecting the conditions. This study can provide reference for the scientific and rational use of straw to achieve ammonia volatilization emission reduction in farmland.

[Effect of Water-Fertilizer-Gas Coupling on Soil N2O Emission and Yield in Greenhouse Tomato].

To reveal the effect of water, fertilizer, and gas coupling on soil N2O emissions in greenhouse tomato soil and suggest appropriate measures for increasing yield and reducing N2O emissions, static chamber-gas chromatography was used to study the effects of soil N2O emissions. The variation laws of soil temperature, water-filled pore space (WFPS), NO3--N content, and O2 content and the influence mechanism of N2O emission under the condition of water-fertilizer-gas coupling were analyzed. Aerated conditions comprised two water levels, 0.6 W and 1.0 W (representing 40% deficit irrigation and full irrigation, W represents when sufficient irrigation water was available), and three nitrogen levels (120 kg·hm-2, 180 kg·hm-2, and 240 kg·hm-2, representing low, medium, and high nitrogen, respectively, with 50% F, 75% F, and F, F is the recommended amount of nitrogen application locally). Three levels of fertilization were used as controlled unaerated full irrigation (O representing aeration, and CK representing conventional drip irrigation). Nine treatments were designed in the experiment. The results showed that the tomato field cumulative emission of N2O under full irrigation (W2F1O, W2F2O, and W2F3O) increased by an average of 55.7% compared with the corresponding treatment at W1 level (P<0.05). The N2O emissions of W1F3O, W2F3O, and W2F3CK fields significantly increased by 13.4% and 43.8% compared with medium nitrogen W1F2O, W2F2O, and W2F2CK and low nitrogen W1F1O, W2F1O, and W2F1CK treatments, respectively (P<0.05).Compared with the corresponding unaerated full irrigation, the emissions (W2F1O, W2F2O, and W2F3O) significantly increased by 11.2% (P<0.05). Aeration, the increase of nitrogen rate, and irrigation amount resulted in the increment of tomato yield and yield-scaled N2O emissions. Compared with medium nitrogen, the yield and yield-scaled N2O emission of high nitrogen treatment increased by 12.5% (P<0.05) and 3.9% (P>0.05), respectively. Compared with low nitrogen treatment, the yield and yield-scaled N2O emission of high nitrogen treatment increased by 30.4% and 9.6% (P<0.05), respectively. The yield and yield-scaled N2O emissions of aerated full irrigation significantly increased by 29.7% and 18.7%, respectively, compared with aerated deficient irrigation. Compared with unaerated irrigation treatment, the yield under aerated treatment increased by 10.4% (P<0.05), and the yield-scaled N2O emission increased by 3.9% (P>0.05). Under the conditions of increasing irrigation water, decreasing fertilizer application, and aeration, partial factor productivity, and irrigation water use efficiency (IWUE) can be significantly increased. After comprehensive consideration of cumulative N2O emissions, tomato production, nitrogen fertilizer utilization efficiency, IWUE, and yield-scaled N2O emission, it can be concluded that aerated low nitrogen full irrigation is an optimal management mode. The results provide reference for increasing yield and reducing emissions of greenhouse tomato.

[Effects of irrigation amounts on soil CO2, N2O and CH4 emissions in greenhouse tomato field.] / 灌水量对温室番茄土壤CO2、N2O和CH4排放的影响.

To understand the effects of different irrigation amounts on soil CO2, N2O, and CH4 emission characteristics and tomato yield, and further put forward effective reduction measures, we carried out an experiment with three irrigation levels: full irrigation (1.0W, W1.0; W meant irrigation amount needed to provide the adequate water), 20% deficit irrigation (0.8W, W0.8) and 40% deficit irrigation (0.6W, W0.6). We used static closed chamber and gas chromatography method to measure greenhouse gas emission in two consecutive greenhouse tomato rotation cycles from April to December, 2017. The results showed that cumulative soil CO2, N2O and CH4 emissions increased with increasing irrigation amounts in the two growing seasons (W1.0＞W0.8＞W0.6), and significant difference of N2O between W0.6 and W1.0 was observed, while other treatment effects on soil gas emissions were not obvious. Compared to W1.0, cumulative soil CO2 emissions were decreased by 12.2% and 8.3%, cumulative soil N2O emissions were decreased by 19.1% and 8.0%, and cumulative soil CH4 emissions were reduced by 11.0% and 6.2% for W0.6 and W0.8, respectively. Tomato yield and global warming potential of soil N2O and CH4 emissions (GWP) increased as irrigation amount increasing. Compared with W1.0, W0.6 significantly decreased tomato yield by 17.0% and GWP by 22.9%, while the difference between the effects of W0.8 and W1.0 on these two parameters was not significant. Global warming potential per tomato yield presented an increase then a decrease as irrigation amount increasing (W0.8＞W1.0＞W0.6), but without stanificance. Irrigation water use efficiency (IWUE) showed a decrease with increasing irrigation amount. Compared with W1.0, IWUE under W0.6 and W0.8 was increased by 38.3% and 9.4%, respectively. Soil CO2 flux was nega-tively and exponentially correlated with soil moisture. The dependence of soil CH4 flux on soil moisture showed a significantly positive correlation. An exponential negative correlation was observed between the soil N2O ux and soil temperature when soil temperature was below or above 18 ℃. Irrigation increased tomato yield and soil greenhouse gas emissions, but decreased IWUE. Therefore, W0.8 was the best mode of irrigation management when synthetically considering tomato yield, IWUE, and greenhouse effect.

[Effects of Water Deficit on Greenhouse Gas Emission in Wheat Field in Different Periods].

Field experiments and static chamber-gas chromatography analysis were conducted in 2016-2017 to study the effects of deficit irrigation on CO2, N2O, and CH4 emissions from soils of winter wheat fields and to optimize irrigation management measures in the Guanzhong Plain of China. Three irrigation levels (full irrigation, 100%; medium water deficit, 80%; and severe water deficit, 60%) were set during the three important growth periods of winter wheat (overwintering, jointing to heading, and heading to filling periods), with 6 distinct treatments (CK, T1, T2, T3, T4, T5, in which CK treatment is full irrigation, and others are water deficit treatments). The dynamic characteristics of the emission fluxes of the three greenhouse gases were described. Crop yield, long-term net global warming potential (net GWPL), and seasonal net global warming potential (net GWPS) were used to comprehensively evaluate the influence of water deficit levels during different growth periods of wheat on economic and ecological issues in the Guanzhong Plain. The results showed that the CO2 and N2O emission fluxes increased, with the highest values for CK treatment. The CH4 absorption fluxes decreased rapidly with increased irrigation, there was even indication of CH4 emissions during high irrigation treatment. Compared to CK treatment, T1, T2, T3, T4, and T5 CO2 emissions decreased significantly by 13.32%, 25.98%, 5.55%, 15.47%, and 17.52% (P<0.05); and N2O emissions decreased by 12.20%, 18.00%, 5.63%, 11.54%, and 13.53%(P<0.05), respectively. The total CH4 absorption significantly increased by 46.47%, 75.78%, 19.47%, 53.40%, and 62.33%(P<0.05), respectively. Net GWPL for T1, T2, T3, T4, and T5 treatments were significantly reduced by 10.07%, 12.77%, 6.50%, 6.81%, and 11.53% (P<0.05), respectively, in comparison with CK treatment. In addition to T3 treatment, net GWPS of T1, T2, T4, and T5 treatments decreased significantly by 13.21%, 37.65%, 24.60%, and 19.86% (P<0.05), respectively, compared with CK. Wheat yield at T1, T2, T3, T4, and T5 treatments reduced significantly by 12.56%, 32.53%, 2.25%, 20.93%, and 18.14% compared with CK treatment (P<0.05). Even though wheat yield under T3 treatment was reduced by 2.25% compared with CK treatment, there was no significant difference (P>0.05). In addition, there were highly significant (P<0.01) positive partial correlations between CO2, N2O, and CH4 emission fluxes and soil WFPS. Therefore, deficient irrigation can significantly reduce greenhouse gas emissions in wheat fields, but there are varying degrees of reduction. Considering both economic and ecological effects of water deficit in different growth periods, T3 treatment is the most conducive to keep the balance between production yield, water conservation, and emission reduction of winter wheat crops in the Guanzhong Plain.

[Estimation of Fraction of Absorbed Photosynthetically Active Radiation for Winter Wheat Based on Hyperspectral Characteristic Parameters].

Estimating fraction of absorbed photosynthetically active radiation (FPAR) precisely has great importance for detecting vegetation water content, energy and carbon cycle balance. Based on this, ASD FieldSpec 3 and SunScan canopy analyzer were applied to measure the canopy spectral reflectance and photosynthetically active radiation over whole growth stage of winter wheat. Canopy reflectance spectral data was used to build up 24 hyperspectral characteristic parameters and the correlation between FPAR and different spectral characteristic parameters were analyzed to establish the estimation model of FPAR for winter wheat. The results indicated that there were extremely significant correlations (p<0.01) between FPAR and hyperspectral characteristic parameters except the slope of blue edge (Db). The correlation coefficient between FPAR and the ratio of red edge area to blue edge area (VI4) was the highest, reaching at 0.836. Seven spectral parameters with higher correlation coefficient were selected to establish optimal linear and nonlinear estimation models of FPAR, and the best estimating models of FPAR were obtained by accuracy analysis. For the linear model, the inversin model between green edge and FPAR was the best, with R2, RMSE and RRMSE of predicted model reaching 0.679, 0.111 and 20.82% respectively. For the nonlinear model, the inversion model between VI2 (normalized ratio of green peak to red valley of reflectivity) and FPAR was the best, with R2, RMSE and RRMSE of predicted model reaching 0.724, 0.088 and 21.84% for. In order to further improve the precision of the model, the multiple linear regression and BP neural network methods were used to establish models with multiple high spectral parameters BP neural network model (R2=0.906, RMSE=0.08, RRMSE=16.57%) could significantly improve the inversion precision compared with the single variable model. The results show that using hyperspectral characteristic parameters to estimate FPAR of winter wheat is feasible. It provides a new method and theoretical basis for monitoring the dynamic change of FPAR in real time, effectively and accurately during the growth stage of winter wheat.

[Application of stationary wavelet transformation to winter wheat SPAD hyperspectral monitoring].

By field trials, the canopy hyperspectral reflectance and chlorophyll content (SPAD) for winter wheat during 2010 and 2011 growth periods were measured by the ASD portable spectrometer and portable chlorophyll meter SPAD-502, respectively. The canopy spectral characteristics of different SPAD values were analyzed in different growth periods. The winter wheat SPAD estimation models based on normalized difference vegetation index (NDVI), ratio vegetation index (RVI) and wavelet energy coefficients were established in different growth periods. The results showed that green peak and red valley characteristics became more and more obvious with the increase of the SPAD. The SPAD estimation models based on NDVI performed better at the regreening stage, elongation stage, heading stage and filling stage with determination coefficients (R2) being 0.7957, 0.8096, 0.7557 and 0.5033, respectively. The winter wheat SPAD estimation models based on wavelet energy coefficients could greatly improve the SPAD estimation accuracy, with regression determination coefficients (R2) of the PVC estimation models based on high frequency energy coefficient and low frequency energy coefficient being 0.9168, 0.9154, 0.8802 and 0.9087 at the regreening stage, elongation stage, heading stage and filling stage, respectively.

[Effects of water deficit at seedling stage on maize root development and anatomical structure].

A pot experiment was conducted to study the effects of water deficit at seedling stage on the root development and anatomical structure of maize. Four treatments were installed, i.e., 75%-85% of field capacity (control), 65%-75% of field capacity (light deficit), 55%-65% of field capacity (moderate deficit), and 45%-55% of field capacity (heavy deficit). Drought stress inhibited the plant growth. With increasing drought stress, the root length, diameter, and total biomass reduced, while the root vigor, root/shoot ratio, and root apex polysaccharide content increased. Under moderate water deficit, the branch root hair length, root hair density, and total length of root hair reached to the maximum. Anatomical observation showed that the decrease of root diameter was mainly due to the decrease of root central cylinder area and of root vessel diameter. No significant difference was observed in the root vessel number among the treatments, but the root vessel wall became irregular under water deficit. The increase of root apex polysaccharide content mainly occurred in the epidermal cells and pileorhiza cells. In epidermis cells, the polysaccharide was mainly in dissociation, while in pileorhiza cells, polysaccharide was mainly as starch grains. In sum, under water deficit, maize root could alter its vessel structure, increase the polysaccharide content in epidermal cells and pileorhiza cells, and expand the total surface area of root hair to enhance the water-absorbing ability of hair root, and to strengthen the drought resistance of maize. However, with the increase of water deficit, root hair didn't have unrestrictive growth, while in adverse, its growth was inhibited or damaged under severe drought.

[Calculation of crop evapotranspiration in greenhouse].

Based on Penman-Monteith equation, a simplified formula for calculating the crop evapotranspiration in greenhouse was deduced by introducing the parameter of crop canopy height and modifying the item of aerodynamics related to wind velocity. The deductive procedure was analyzed theoretically, and the formula was validated with meteorological data. The results showed that the modified Penman-Monteith equation had a higher precision of prediction, with a relative deviation of 4. 7%-17. 1% and 11. 1% on average, being suitable to calculate the crop evapotranspiration in greenhouse.